This invention relates to thermoplastic rubber compositions, to the preparation of thermoplastic rubber compostions, and to products made therefrom.
Thermoplastic rubbers are a class of polymers which behave as crosslinked materials at ambient temperatures but display the characteristics of thermoplastic materials at elevated temperatures. A class of thermoplastic rubbers which can be distinguished from the conventional hydrocarbon block copolymer type of thermoplastic rubbers, are the elastomeric ionomers. These thermoplastic rubbers are elastomeric polymers carrying one or more pendant ionic or inorganic salt groups along the polymer backbone. These ionic groups can interact with one another, thereby forming ion-rich aggregates contained in a non-polar polymeric medium.
Elastomeric ionomers are generally formed from elastomeric polymers having one or more acid or acid-reacting groups, such as sulfonic acid or carboxylic acid groups. Such sulfonic acid group-containing elastomers may conveniently be obtained via a direct sulfonation of a preformed, suitable elastomer, for example, an elastomer containing olefinic unsaturated groups and/or arene groups. Carboxylic acid group-containing elastomers may conveniently be prepared by copolymerizing one or more olefinically unsaturated carboxylic acids, such as acrylic or methacrylic acid, with one or more other suitable olefinically unsaturated monomers. However, as the copolymerization is generally conducted in the presence of a radical or redox initiator system, it will generally yield polymers having an incorrect balance of molecular weight and molecular weight distribution for application in thermoplastic rubber compositions.
An alternative method for the preparation of carboxylated elastomers would be the introduction of carboxyl groups via grafting of a suitable olefinically unsaturated carboxylic acid or anhydride, such as maleic anhydride, onto a preformed elastomer. However, it was found that the ionomers obtained by neutralizing such carboxylated elastomers were characterized by insufficient flow at elevated temperature and low tensile strength.
It is therefore an object of the invention to provide improved thermoplastic rubber compositions based on carboxylated elastomeric polymers. It is still another object of the invention to provide thermoplastic rubber compositions based on carboxylated elastomeric polymers which have high flow at elevated temperature, and good tensile strength. It is still another object of the invention to provide a process for making thermoplastic rubber compositions based on elastomeric polymers.